Method and apparatus for transmitting and receiving system information in a mobile communication system

ABSTRACT

A method and apparatus are provided for transmitting and receiving System Information (SI) in a mobile communication system. The method for receiving the SI by a User Equipment (UE) includes receiving, by the UE, at a fixedly scheduled sub-frame of a predetermined radio frame within a Primary Broadcast CHannel (P-BCH) transmission period, the SI including first partial bits of a System Frame Number (SFN), the first partial bits indicating a repeated value; and acquiring, by the UE, second partial bits of the SFN in the predetermined radio frame by decoding the P-BCH, the second partial bits indicating a different value.

PRIORITY

This application is a Continuation of U.S. application Ser. No.12/027,542, which issued as U.S. Pat. No. 8,169,986 on May 1, 2012, andclaims priority under 35 U.S.C. §119(a) to Korean Patent ApplicationSerial No. 2007-13863, which was filed in the Korean IntellectualProperty Office on Feb. 9, 2007, the entire disclosure of each of whichis hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a mobile communicationsystem. More particularly, the present invention relates to a method forefficiently broadcasting system information in a cell and a method forreceiving the system information in a User Equipment (UE).

2. Description of the Related Art

The Universal Mobile Telecommunications System (UMTS) is a 3^(rd)Generation (3G) asynchronous mobile communication system operating inWideband Code Division Multiple Access (WCDMA), based on European mobilecommunication systems, Global System for Mobile Communications (GSM) andGeneral Packet Radio Services (GPRS). The 3^(rd) Generation PartnershipProject (3GPP) that standardized UMTS is now discussing Long TermEvolution (LTE) as the next generation of UMTS, known as Evolved UMTS.The 3GPP LTE is a technology for enabling packet communications at orabove 100 Mbps, aiming at commercialization by 2010. For deploying theLTE system, many communication schemes have been proposed. Among themare schemes of reducing the number of nodes on a communication line bysimplifying a network configuration or of optimizing radio protocols forradio channels.

FIG. 1 is a diagram illustrating an Evolved UMTS system to which thepresent invention is applied.

Referring to FIG. 1, each of Evolved UMTS Radio Access Networks(E-UTRANs or E-RANs) 110 is simplified to a 2-node structure includingEvolved Node Bs (ENBs) 120 and 122 and an anchor node 130, or ENBs 124,126 and 128 and an anchor node 132. A User Equipment (UE) 101 isconnected to an Internet Protocol (IP) network 114 via the E-UTRAN 110.The ENBs 120 to 128 correspond to legacy Node Bs in the UMTS system andare connected to the UE 101 via radio channels. Compared to the legacyNode Bs, the ENBs 120 to 128 play a more complex role. Since all usertraffic including real-time service such as Voice Over IP (VoIP) isserviced on shared channels in the 3GPP LTE, an entity for collectingthe status information of UEs and scheduling them is required and theENBs 120 to 128 are responsible for the scheduling. Generally, an ENBcontrols a plurality of cells. Generally, the ENBs 120 to 128 performAdaptive Modulation and Coding (AMC) by adaptively selecting amodulation scheme and a channel coding rate for a UE according to thechannel status of the UE. As with High Speed Downlink Packet Access(HSDPA) and High Speed Uplink Packet Access (HSUPA) of UMTS (alsoreferred to as Enhanced Dedicated CHannel (EDCH)), the LTE system usesHybrid Automatic Repeat reQuest (HARQ) between the ENBs 120 to 128 andthe UE 101. Considering that a variety of Quality of Service (QoS)requirements cannot be fulfilled with HARQ alone, a high layer mayperform an outer ARQ between the UE 101 and the ENBs 120 to 128. HARQ isa technique for increasing reception success rate by soft-combiningprevious received data with retransmitted data without discarding theprevious data. High-speed packet communication systems such as HSDPA andEDCH use HARQ to increase transmission efficiency. To realize a datarate of up to 100 Mbps, it is expected that the LTE system will adoptOrthogonal Frequency Division Multiplexing (OFDM) in a 20-MHz bandwidthas a radio access technology.

FIG. 2 illustrates system information broadcast in cells.

Referring to FIG. 2, reference numeral 201 denotes an ENB and referencenumerals 211, 213 and 215 denote transmissions of system informationfrom first, second and third cells, CELL #1, CELL #2 and CELL #3,respectively. The system information includes essential physicalparameters and high-layer parameters common to UEs in a cell so that theUEs can receive a service in the cell. The physical parameters include,but are not limited to, the bandwidth of the cell, a Cyclic Prefix (CP)length, a physical channel configuration, the number of transmitantennas, and a System Frame Number (SFN), for example. The high-layerparameters may include a measurement Identifier (ID) and schedulinginformation about frequency or time resources in which other high-layerparameters are transmitted. A Primary Broadcast CHannel (P-BCH) carriesthe system information. To stably reach a cell boundary, the P-BCH needsa high transmit power or a robust Modulation and Coding Scheme (MCS)level.

FIG. 3 illustrates an exemplary method for transmitting systeminformation.

Referring to FIG. 3, a 10-ms radio frame 301 includes ten subframes 303.It is assumed herein that a P-BCH carries system information in a1.25-MHz subframe in every radio frame. As described before withreference to FIG. 2, to stably reach a cell boundary, the P-BCH carriesa limited number of bits in a subframe. For example, a very low codingrate is applied to the P-BCH to achieve a 1% BLock Error Rate (BLER) for98% of the cell coverage area and the P-BCH may deliver no more than 20to 30 bits of information in a 1-ms subframe with a 1.25 MHz ofbandwidth. The limitation on the number of P-BCH information bits makesit impossible to transmit all of the necessary system information on theP-BCH. If system information is ever managed to fit the allowed numberof information bits, the system information size cannot be extended forthe next transmission on the P-BCH. Accordingly, there is a need for amethod for transmitting more information bits on the P-BCH in a givenbandwidth.

SUMMARY OF THE INVENTION

The present invention is to address at least the problems and/ordisadvantages described above and to provide at least the advantagesdescribed below.

Accordingly, an aspect of the present invention is to provide a methodand apparatus for transmitting a greater number of information bits on aP-BCH with a predetermined bandwidth in a cell and a method andapparatus for receiving system information in a UE.

In accordance with an aspect of the present invention, a method forreceiving System Information (SI) by a User Equipment (UE) in a mobilecommunication system is provided. The method includes receiving, by theUE, at a fixedly scheduled sub-frame of a predetermined radio framewithin a Primary Broadcast CHannel (P-BCH) transmission period, the SIincluding first partial bits of a System Frame Number (SFN), the firstpartial bits indicating a repeated value; and acquiring, by the UE,second partial bits of the SFN in the predetermined radio frame bydecoding the P-BCH, the second partial bits indicating different values.

In accordance with another aspect of the present invention, a method fortransmitting SI by a Node B in a mobile communication system isprovided. The method includes encoding, by the Node B, second partialbits of an SFN in a predetermined radio frame within a P-BCHtransmission period, the second partial bits indicating differentvalues; and transmitting, by the Node B, at a fixedly scheduledsub-frame of the predetermined radio frame, the encoded second partialbits and the SI including first partial bits of the SFN, the firstpartial bits indicating a repeated value

In accordance with another aspect of the present invention, a UE isprovided for receiving SI in a mobile communication system. The UEincludes a receiver that receives, at a fixedly scheduled sub-frame of apredetermined radio frame within a P-BCH transmission period, the SIincluding first partial bits of an SFN, the first partial bitsindicating a repeated value; and a controller that acquires secondpartial bits of the SFN in the predetermined radio frame after decodingthe P-BCH, the second partial bits indicating different values.

In accordance with another aspect of the present invention, a Node B isprovided for transmitting SI in a mobile communication system. The NodeB includes an encoder that encodes second partial bits of an SFN in apredetermined radio frame within a P-BCH transmission period, the secondpartial bits indicating different values; and a transmitter thattransmits the encoded second partial bits and the SI including firstpartial bits of the SFN at a fixedly scheduled sub-frame of thepredetermined radio frame, the first partial bits indicating a repeatedvalue.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a 3GPP LTE system according to an embodiment of thepresent invention;

FIG. 2 illustrates system information broadcast in cells;

FIG. 3 illustrates a method for transmitting system information;

FIG. 4 is a diagram illustrating a method for transmitting systeminformation and a method for receiving the system information in a UEaccording to an embodiment of the present invention;

FIG. 5 is a flowchart of an operation of an ENB according to anembodiment of the present invention;

FIG. 6 is a block diagram of an ENB apparatus according to an embodimentof the present invention;

FIG. 7 is a flowchart of an operation of the UE according to anembodiment of the present invention;

FIG. 8 is a block diagram of a UE apparatus according to an embodimentof the present invention;

FIG. 9 is a diagram illustrating a method for transmitting systeminformation and a method for receiving the system information in the UEaccording to an embodiment of the present invention;

FIG. 10 is a flowchart of an operation of the ENB according to anembodiment of the present invention;

FIG. 11 is a block diagram of an ENB apparatus according to anembodiment of the present invention;

FIGS. 12A and 12B are a flowchart of an operation of the UE according toan embodiment of the present invention; and

FIG. 13 is a block diagram of a UE apparatus according to an embodimentof the present invention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The matters defined in the description such as detailed constructionsand elements are provided to assist in a comprehensive understanding ofcertain embodiments of the invention. Accordingly, those of ordinaryskill in the art will recognize that various changes and modificationsof the embodiments described herein can be made without departing fromthe scope and spirit of the invention. Also, descriptions of well-knownfunctions and constructions are omitted for clarity and conciseness.

While certain embodiments of the present invention will be described inthe context of a 3GPP LTE system evolved from a 3GPP UMTS system, it isto be clearly understood that the present invention is applicable toother mobile communication systems as well.

FIG. 4 is a diagram illustrating a method for transmitting systeminformation and a method for receiving the system information in a UEaccording to an exemplary embodiment of the present invention.

Referring to FIG. 4, it is assumed herein that a 10-ms radio frame 401includes ten subframes 403 and a P-BCH carries system information in a1.25-MHz subframe of every radio frame. Reference numeral 411 denotes anSFN encoded in a predetermined coding scheme and transmitted inpredetermined resources of the 1.25-MHz subframe. The resources can befrequency resources, a scrambling code, or the like. Reference numeral413 denotes P-BCH information that has the same value during a P-BCHtransmission period other than the SFNs. The P-BCH information 413 isencoded in a different coding scheme/coding rate from that of the SFN411 and transmitted in different resources from those of the SFN 411 inthe 1.25 MHz subframe.

If a UE receives system information from an ENB at a P-BCH transmissiontime 421, the UE acquires an SFN 431, SFN #1000, and the P-BCHinformation 413 by decoding and interpreting the system information inpredetermined resources of 1.25 MHz (i.e. SFN transmission resources andother P-BCH transmission resources) according to a predetermined method.If the UE fails to receive the P-BCH information 413 at the P-BCHtransmission time 421, that is, the P-BCH information 413 turns out tohave errors in a Cyclic Redundancy Check (CRC) check, the UE stores theP-BCH information 413 in a buffer, receives the P-BCH information 413 atthe next P-BCH transmission time 423, and combines the stored P-BCHinformation 413 with the received P-BCH information 413.

The UE checks the continuity of SFNs received and decoded/interpreted atthe P-BCH transmission times 421 and 423, to thereby detect and correctreception errors in the SFNs if there are any reception errors. Forinstance, if the SFNs are #1000 and #1001, they are successive, whichimplies successful reception of the SFNs 431 and 433. Thus, the UEapplies the SFNs, considering that the SFNs have been successfullyacquired. On the other hand, if the SFNs are not successive (e.g. #1000and #1200), the UE receives an SFN 435 at the next P-BCH transmissiontime 425 and detects and corrects reception errors in the SFNs. If theSFN 435 is #1002, the UE determines that SFN #1200 received at the P-BCHtransmission time 423 is wrong and corrects the SFN to #1001.

FIG. 5 is a flowchart of an operation of an ENB according to theexemplary embodiment of the present invention.

Referring to FIG. 5, when determining to transmit P-BCH information andan SFN in step 501, the ENB encodes the P-BCH information and the SFN inpredetermined coding methods/coding rates in step 511 and transmits theencoded P-BCH information and SFN in respective predeterminedfrequency/time resources in step 513. Considering that a UE will combinethe P-BCH information, the ENB transmits the P-BCH at a lower transmitpower level or using an appropriate MCS level so that the P-BCH cancarry more information bits.

FIG. 6 is a block diagram of an ENB apparatus according to the exemplaryembodiment of the present invention.

Referring to FIG. 6, an SFN manager 601 is a function block forcontrolling and managing SFNs. The SFN manager 601 increases an SFNevery radio frame. A P-BCH manager 603 controls and manages P-BCHinformation other than the SFNs. A coder 621 encodes the SFNs and theP-BCH information at predetermined respective coding rates according topredetermined respective coding methods. A controller 611 controlstransmission timings of the SFNs and the P-BCH information from the SFNmanager 601 and the P-BCH manager 603 and controls the coding methodsand coding rates of the coder 621. A transmitter 631 transmits the codedSFNs and the P-BCH information received from the coder 621 to a cell.

FIG. 7 is a flowchart of an operation of the UE according to theexemplary embodiment of the present invention.

Referring to FIG. 7, when determining that an SFN or P-BCH informationneeds to be received in step 701, the UE determines in step 711 whetherSFN information of a serving cell has been acquired. If the SFNinformation has not been acquired, the UE receives in step 731 an SFNand P-BCH information in predetermined respective resources usingpredetermined respective coding methods/coding rates.

In step 733, the UE determines whether the P-BCH information has beensuccessfully received by such as CRC error. If the P-BCH information hasbeen successfully received, the UE receives in step 751N SFNs (N>=1) innext P-BCH transmission period and detects and corrects in step 753 SFNreception errors by checking the continuity of the received SFNs. Forexample, for N=1, if the SFN received in step 731 is SFN #1000 and theSFN received in step 751 is SFN #1001, the UE determines that the SFNinformation has been successfully acquired because the SFNs aresuccessive. For N=2, if the SFN received in step 731 is SFN #1000 andthe SFNs received in step 751 are SFN #1200 and SFN #1002, the UEdetermines that SFN #1200 is incorrect and corrects this SFN to #1001.

In step 755, the UE checks the continuity of ordered SFNs resulting fromstep 753 and determines whether the SFN information has beensuccessfully received. If the ordered SFNs are successive, the UEapplies in step 757 the SFNs, considering that the SFN information hasbeen successfully acquired. If it is determined in step 755 that the SFNinformation acquisition has been failed, the UE returns to step 751 andrepeats 751 to 755.

If a CRC has occurred to the P-BCH information in step 733, the UEreceives in step 741 an SFN and P-BCH information in the nexttransmission period and combines in step 743 the received P-BCHinformation with P-BCH information received in a previous transmissionperiod. In step 745, the UE checks the result of the combining. If thecombining result tells that the P-BCH information has been successfullyreceived (i.e. without a CRC error), the UE goes to step 753. If thereception of the P-BCH information failed (i.e. a CRC error hasoccurred), the UE returns to step 741.

If the UE has already acquired the SFN information of the cell in step711, the UE receives in step 721 only P-BCH information in predeterminedresources using a predetermined coding method and coding rate. If the UEhas failed to receive the P-BCH information successfully, in step 723the UE receives P-BCH information in the next transmission period andcombines the received P-BCH information with previous P-BCH information.

FIG. 8 is a block diagram of a UE apparatus according to the exemplaryembodiment of the present invention.

Referring to FIG. 8, a receiver 811 receives system information from acell. A controller 821 controls the application of a decoding method anda decoding rate to the system information. The controller 821 performsthe control operation so that different decoding methods and decodingrates are applied to the SFN and P-BCH information. A decoder 831decodes the SFN and the P-BCH information under the control of thecontroller 821 and provides the decoded SFN to an SFN manager 841 andthe decoded P-BCH information to a P-BCH manager 843. The SFN manager841 checks the continuity of received SFNs and according to the result,the SFN manager 841 can additionally receive SFNs in next transmissionperiods through the controller 821. If the P-BCH information receptionfailed, the P-BCH manager 843 stores the received P-BCH information in abuffer 845 and combines the stored P-BCH information with P-BCHinformation received in the next transmission period.

FIG. 9 is a diagram illustrating a method for transmitting systeminformation and a method for receiving the system information in the UEaccording to another exemplary embodiment of the present invention.

Referring to FIG. 9, it is assumed herein that a 10-ms radio frame 901includes ten subframes 903 and a P-BCH carries system information in a1.25-MHz subframe of every radio frame. Reference numeral 911 denotes anSFN offset encoded in a predetermined coding scheme and transmitted inpredetermined resources in the 1.25-MHz subframe. The resources can befrequency resources, a scrambling code, or the like. Reference numeral913 denotes P-BCH information. The P-BCH information 913 is encoded in adifferent coding scheme/coding rate from that of the SFN offset 911 andtransmitted in different resources from those of the SFN offset 911 inthe 1.25 MHz subframe. The coding method can be repetition. The P-BCHinformation 913 includes a reference SFN instead of an actual SFN. Thereference SFN is identical during one SFN offset period. The actual SFNis obtained by adding the reference SFN and an SFN offset.

For example, if an actual SFN is #1000 at time 921 and an SFN offset isrepresented in two bits, the SFN offset is one of {0, 1, 2, 3} and areference SFN is kept to be #1000 during one SFN offset period. The SFNoffset and the reference SFN are carried on the P-BCH. That is, theP-BCH delivers the same reference SFN, SFN #1000, in radio frames havingSFN #1000 to SFN #1003, and SNF offsets 0, 1, 2 and 3, respectively, atthe transmission times of SFN #1000 to SFN #1003. Since the samereference SFN, SFN #1000 applies to the radio frames SFN #1000 to SFN#1003, the UE can combine P-BCH information received in the radio framesSFN #1000 to SFN #1003. As described before, an actual SFN is calculatedby adding a reference SFN and an SFN offset received on the P-BCH in aradio frame.

If the UE receives system information at a P-BCH transmission time 921,the UE acquires an SFN offset 931, SFN offset 0, by decoding andinterpreting the system information in predetermined resources of 1.25MHz (i.e. SFN transmission resources and other P-BCH transmissionresources) according to a predetermined method. If the UE fails toreceive the P-BCH information 913, that is, the P-BCH information 913has a CRC error, the UE stores the P-BCH information 913 in a buffer,receives the P-BCH information 913 at the next P-BCH transmission time923, and combines the stored P-BCH information 913 with the receivedP-BCH information 913.

The UE receives an SFN offset 933, SFN offset 1 at the P-BCHtransmission time 923 and SFN offset 1 is successive to SFN offset 0.Therefore, the UE determines that the SFN offsets have been receivedwithout errors. Since the P-BCH information 913 received at the P-BCHtransmission times 921 and 923 includes the same reference SFN, the UEcan combine the P-BCH information 913.

In the case where an SFN offset received at the current P-BCHtransmission time is one SFN offset period away from an SFN offset ofthe previous P-BCH transmission time, for example, when previous andcurrent 2-bit SFN offsets are 3 and 0, respectively, P-BCH informationreceived at the two P-BCH transmission times cannot be combined. Then,the UE clears its buffer and performs a CRC check on the P-BCHinformation received at the current P-BCH transmission time withoutcombining. If the CRC check is bad, i.e. turns up errors, the UE storesthe P-BCH information in the buffer and can correct the error in theP-BCH information using next-received P-BCH information.

If the SFN offsets received at the P-BCH transmission times 921 and 923are not successive, the UE cannot determine whether the received P-BCHinformation is within the same SFN offset period. In this case, the UEperforms a CRC check on the P-BCH information received at the P-BCHtransmission time 923. If the CRC check is bad, the UE combines theP-BCH information with the P-BCH information received at the P-BCHtransmission time 921 and then checks a CRC in the combined P-BCHinformation. It can be further contemplated that the P-BCH informationreceived at the P-BCH transmission times 921 and 923 are first combinedand then CRC-checked, and if the CRC check is bad, the P-BCH informationreceived at the P-BCH transmission time 923 is separately CRC-checked.It can also be further contemplated that the P-BCH information receivedat the P-BCH transmission times 921 and 923 are combinedunconditionally.

If the UE cannot decide as to the continuity of the SFN offsets at anyof the P-BCH transmission times 921, 923 and 925, the UE combines P-BCHinformation received at the next P-BCH transmission time 925 with theP-BCH information received at the P-BCH transmission times 921 and 923in all possible cases and performs a CRC check on the combined P-BCHinformation. For example, the UE combines the P-BCH information receivedat the next P-BCH transmission time 925 with the P-BCH informationreceived at the P-BCH transmission time 921, combines the P-BCHinformation received at the next P-BCH transmission time 925 with theP-BCH information received at the P-BCH transmission time 923, andperforms a CRC check on the combined information in every possible case.

If the P-BCH signal has been successfully received by combining at theP-BCH transmission time 923, the UE obtains the actual SFN, SFN #1000for the P-NCH transmission time 921 by adding the reference SFN, SFN#1000, included in the P-BCH signal to SFN offset 0 for the P-BCHtransmission time 921 and obtains the actual SFN, SFN #1001, for theP-NCH transmission time 923 by adding the reference SFN, SFN #1000, toSFN offset 1 for the P-BCH transmission time 923.

The UE can detect and correct reception errors by checking thecontinuity of N (N>=2) received SFN offsets. For example, for N=2, ifSFN offsets 0 and 1 are received at the P-BCH transmission times 921 and923, respectively, the UE determines that the SFN information has beensuccessfully received because SFN offsets 0 and 1 are successive. In thesame manner, for N=3, if SFN offsets 0, 2 and 2 are received at theP-BCH transmission times 921, 923 and 925, respectively, the UEdetermines that SFN offset 2 received at the P-BCH transmission time 923is wrong and corrects this SFN offset to 1 using the previous and nextSFN offsets.

While not shown, the UE can combine P-BCH information over everypossible case (blind combining) and detect SFN offsets according to thecombining results. For example, if a 1-bit SFN offset is used and the UEcannot decide as to the continuity of SFN offsets, the UE performs blindcombining. If a CRC error is not detected from a certain combining case,the SFN offsets of two successive pieces of P-BCH information in thesuccessful combining case are 0 and 1, sequentially. That is, if SFNoffsets are represented in one bit, the P-BCH information received atthe P-BCH transmission times 921, 923 and 925 is combined in everypossible case. If no CRC error is found in the combination of the P-BCHinformation received at the P-BCH transmission times 923 and 925, theSFN offsets of the P-BCH transmission times 923 and 925 are 0 and 1,sequentially.

FIG. 10 is a flowchart of an operation of the ENB according to thesecond exemplary embodiment of the present invention.

Referring to FIG. 10, when determining to transmit P-BCH information andan SFN offset in step 1001, the ENB sets the SFN offset in step 1011.For example, if the SFN offset is represented in two bits, the ENB canset the SFN offset mapped to an actual SFN by (SFN mod 4). In step 1013,the ENB determines whether the SFN offset is within one SFN offsetperiod. For example, if an SFN offset is 2 bits and set to be one of 0,1, 2, 3, and 0, an SFN offset set to the second 0 is outside one SFNoffset period. That is, one SFN offset period is a period for which SFNoffsets are set to 0, 1, 2 and 3, sequentially.

If the SFN offset is within one SFN offset period in step 1013, the ENBstill uses a reference SFN included in P-BCH information transmitted atthe previous P-BCH transmission time in step 1021. The reference SFN isset to a value resulting from subtracting the SFN offset from an actualSFN. If the SFN offset is outside one SFN offset period in step 1013,the ENB updates in step 1023 the reference SFN to be included in a P-BCHsignal and in step 1025 encodes the P-BCH and the SFN offset inpredetermined coding methods. Herein, transmit power or an MCS level iscontrolled for P-BCH information including the reference SFNcorresponding to the SFN offset within one SFN offset period, under theassumption that the UE combines the P-BCH information. For example, theENB uses a low transmit power level or an MCS level with a high codingrate for the P-BCH information. In step 1027, the ENB transmits theP-BCH information and the SFN offset in predetermined respectiveresources.

FIG. 11 is a block diagram of an ENB apparatus according to the secondexemplary embodiment of the present invention.

Referring to FIG. 11, the ENB apparatus has the same configuration asthat illustrated in FIG. 6 according to the first exemplary embodimentof the present invention, except for an SFN offset manager 1101. The SFNoffset manager 1101 sets and manages SFN offsets. The SFN offsets areset to {SFN mod 2^((number of bits allocated to SFN offset))}. Acontroller 1111 updates a reference SFN included in P-BCH informationfrom a P-BCH information manager 1103 according to an SFN offset set bythe SFN offset manager 1101, when needed. A coder 1121 encodes the SFNoffset and P-BCH information in predetermined coding methods/codingrates.

FIGS. 12A and 12B are a flowchart of an operation of the UE according tothe second exemplary embodiment of the present invention.

Referring to FIGS. 12A and 12B, when determining that P-BCH informationneeds to be received in step 1201, the UE determines in step 1211whether SFN information of a serving cell has already been acquired. Ifthe SFN information has not been acquired, the UE in step 1241 receivesan SFN offset and P-BCH information in predetermined respectiveresources using predetermined respective coding methods/coding rates. Instep 1243, the UE checks whether the P-BCH information has a CRC error.If the P-BCH information has been successfully received without the CRCerror, the UE receives in step 1251N SFN offsets (N>=1) in next P-BCHtransmission periods, and in step 1253 detects and corrects SFN offsetreception errors by checking the continuity of the received SFN offsets.For example, for N=1, if the SFN offset received in step 1241 is 0 andthe SFN offset received in step 1251 is 1, the UE determines that theSFN offset information has been successfully acquired because the SFNoffsets are successive. For N=2, if the SFN offset received in step 1241is 0 and the SFN offsets received in step 1251 are 3 and 2, the UEdetermines that SFN offset 3 is wrong and corrects this SFN offset to 1.

In step 1255, the UE checks the continuity of the SFN offsets correctedin step 1253 and determines whether the SFN offset information has beensuccessfully acquired. If the SFN offsets are successive, the UE goes tostep 1259, considering that the SFN offset information has beensuccessfully acquired in step 1255. If in step 1255 it is determinedthat the SFN offset information acquisition failed, the UE returns tostep 1251 and repeats 1251 to 1255.

In step 1257, the UE generates actual SFNs by combining a reference SFNincluded in the P-BCH information with the respective SFN offsets instep 1257 and in step 1259 applies the actual SFNs, considering thatacquisition of SFN information of the cell has been completed.

If in step 1243 it is determined that a CRC error has occurred in theP-BCH information, in step 1261 the UE receives a new SFN offset andP-BCH information in the next transmission period. In step 1263, the UEdetects reception errors by checking the continuity of SFN offsetsincluding the new SFN offset and if a reception error is detected, theUE corrects it. The UE determines whether the SFN offset received instep 1261 and corrected in step 1263 is within the same SFN offsetperiod as an SFN offset received in the previous P-BCH transmissionperiod in step 1265. In step 1267, the UE determines whether thereceived or corrected SFN offsets are successive in step 1267. If theSFN offsets are not successive, the UE combines P-BCH information forevery possible case (blind combining) in step 1281. Every possiblecombing case may include the case of no combining. If the SFN offsetsare successive in step 1267, the UE in step 1271 determines whether thesuccessive SFN offsets are within the same SFN offset period. If theyare within the same SFN offset period, the UE in step 1273 combines theP-BCH information received in step 1261 with at least one piece ofpreviously received P-BCH information. If the SFN offsets are within thesame SFN offset period in step 1271, the UE in step 1275 clears thebuffer without combining. After step 1281, 1273, or 1275, the UE returnsto step 1243.

If the UE has already acquired the SFN information of the cell in step1211, the UE in step 1221 receives P-BCH information in predeterminedresources using a predetermined coding method and determines in step1223 whether the P-BCH information has been successfully receivedwithout a CRC error. If a CRC has occurred and the P-BCH informationreception failed, the UE combines in step 1233 the P-BCH informationwith at least one piece of next P-BCH information whose SFN offsets arewithin the same SFN offset period. If the UE receives P-BCH informationwhose SFN offset does not fall within the same SFN offset period, instep 1235 the UE clears the buffer without combining the P-BCHinformation. After step 1235, the UE returns to step 1223.

FIG. 13 is a block diagram of a UE apparatus according to the secondexemplary embodiment of the present invention.

Referring to FIG. 13, the UE apparatus has the same configuration asthat illustrated in FIG. 8 according to the first exemplary embodimentof the present invention, except for an SFN offset manager 1341. Areceiver 1311 receives P-BCH information and an SFN offset from a cell.A controller 1321 controls a decoder 1331 to decode the SFN offset andthe P-BCH information in predetermined respective decoding methods. Thedecoded SFN offset and the decoded P-BCH information are provided to theSFN offset manager 1241 and a P-BCH manager 1343, respectively. The SFNoffset manager 1341 checks the continuity of decoded SFN offsets andaccording to the result. The SFN offset manager 1341 can additionallyreceive SFN offsets at next transmission times through the controller1321. If the P-BCH information reception failed, the P-BCH manager 1343stores the received P-BCH information in a buffer 1345 and combines thestored P-BCH information with at least one piece of P-BCH informationwithin the same SFN offset period, received through the SFN offsetmanager 1341 and the controller 1321. An SFN offset can be transmittedon a physical channel after repetition. The repetition is considered asa kind of coding. In FIG. 13, for the sake of convenience, it is assumedthat the decoder 1331 also interprets the SFN offset which was repeated.

As is apparent from the above description, the present inventionadvantageously enables more P-BCH information bits in a given bandwidthin a cell.

While the invention has been shown and described with reference tocertain exemplary embodiments of the present invention thereof, it willbe understood by those skilled in the art that various changes in formand details may be made therein without departing from the spirit andscope of the present invention as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A method for receiving system information (SI) bya user equipment (UE) in a mobile communication system, the methodcomprising: receiving, by the UE, the SI including first partial bits ofa system frame number (SFN) on a broadcast channel (BCH) at a firstsubframe of a radio frame, the first partial bits of the SFN having anidentical value indicating a reference SFN during a predetermined Nsuccessive radio frames of a BCH transmission period, where N is apositive integer; and acquiring, by the UE, second partial bits of theSFN for the radio frame, the second partial bits of the SFN havingdifferent values in each radio frame of the predetermined N successiveradio frames of the BCH transmission period, and the second partial bitsindicating an offset, wherein the SFN is calculated based on the firstpartial bits and the second partial bits.
 2. The method of claim 1,wherein N is four and the second partial bits of the SFN is two bits. 3.The method of claim 1, wherein the second partial bits of the SFN andthe first partial bits of the SFN are encoded using different resources,respectively.
 4. The method of claim 3, wherein a resource for encodingthe second partial bits of the SFN includes a scrambling code.
 5. Themethod of claim 1, wherein the second partial bits are acquired bydescrambling the SI.
 6. A method for transmitting system information(SI) by a node B in a mobile communication system, the methodcomprising: encoding, by the node B, second partial bits of a systemframe number (SFN) in a radio frame, the second partial bits of the SFNhaving different values in each radio frame of a predetermined Nsuccessive radio frames of a broadcast channel (P-BCH) transmissionperiod, where N is a positive integer; and transmitting, by the Node B,the encoded second partial bits of the SFN and the SI including firstpartial bits of the SFN on a BCH at a first subframe of the radio frame,the first partial bits of the SFN having an identical value indicating areference SFN during the predetermined N successive radio frames of theBCH transmission period, and the second partial bits indicating anoffset, wherein the SFN is calculated based on the first partial bitsand the second partial bits.
 7. The method of claim 6, wherein N is fourand the second partial bits of the SFN is two bits.
 8. The method ofclaim 6, wherein the first partial bits of the SFN and the secondpartial bits of the SFN are encoded using different resources,respectively.
 9. The method of claim 8, wherein a resource for encodingthe second partial bits of the SFN includes a scrambling code.
 10. Auser equipment (UE) for receiving system information (SI) in a mobilecommunication system, the UE comprising: a receiver configured toreceive the SI including first partial bits of a system frame number(SFN) on a broadcast channel (BCH) at a first subframe of a radio frame,the first partial bits of the SFN having an identical value indicating areference SFN during a predetermined N successive radio frames of a BCHtransmission period, where N is a positive integer; and a controllerconfigured to acquire second partial bits of the SFN for the radioframe, the second partial bits of the SFN having different values ineach radio frame of the predetermined N successive radio frames of theBCH transmission period, and the second partial bits indicating anoffset, wherein the SFN is calculated based on the first partial bitsand the second partial bits.
 11. The UE of claim 10, wherein N is fourand the second partial bits of the SFN is two bits.
 12. The UE of claim10, wherein the first partial bits of the SFN and the second partialbits of the SFN are encoded using different resources, respectively. 13.The UE of claim 12, wherein a resource for encoding the second partialbits of the SFN includes a scrambling code.
 14. The UE of claim 10,wherein the second partial bits are acquired by descrambling the SI. 15.A node B for transmitting system information (SI) in a mobilecommunication system, the Node B comprising: an encoder configured toencode second partial bits of a system frame number (SFN) in a radioframe, the second partial bits of the SFN having different values ineach radio frame of a predetermined N successive radio frames of abroadcast channel (BCH) transmission period, where N is a positiveinteger; and a transmitter configured to transmit the encoded secondpartial bits of the SFN and the SI including first partial bits of theSFN on a BCH at a first subframe of the radio frame, the first partialbits of the SFN having an identical value indicating a reference SFNduring the predetermined N successive radio frames of the BCHtransmission period, and the second partial bit indicating an offset,wherein the SFN is calculated based on the first partial bits and thesecond partial bits.
 16. The Node B of claim 15, wherein N is four andthe second partial bits of the SFN is two bits.
 17. The Node B of claim15, wherein the first partial bits of the SFN and the second partialbits of the SFN are encoded using different resources, respectively. 18.The Node B of claim 17, wherein a resource for encoding the secondpartial bits of the SFN includes a scrambling code.